Inhibition of resin growth from diolefins



Oct. 4, 1949. c. E. .MORRELL ET AL 2,433,778

INHIBITION OF RESIN GROWTH FROM DIOLEFINS Filed Aug. 14, 1946 GROWTH oF PoPcoRN 'PoLvMEIa .SEE'D IN SATURATED BU'TAZDVIENE. AT 60 Q. NO OXYGEN W 0 40 .45 E mm; 2 -Cauhflowr 0.20 huhafly E fimalll Ave;

ass 7 010g y g: Q08 (.8 Q 067 80.0%

ime, Davs 61AM am,

Patented Oct. 4, 1949 INHIBITION OF RESIN GROWTH FROM LEFINS DIO Charles E. Morrell, Westfleld, and Richard F. Robey, Cranford, N. 1., assignors to Standard Oil Development Company, a corporation of Delaware Application August, 1946, Serial No. 690,560

6 Claims. (Cl. 260-6665) This invention relates to a process for minimizing or inhibiting the formation and/or growth of solid and semi-solid resins during the separation and segregation of diolefins from other hydrocarbons. It is generally applicable to operations in which diolefinic hydrocarbons are handled.

In the separation and segregation of dioleflns from other hydrocarbons by absorption, desorption and distillation, various types of polymers are formed, that is, dimers, viscous high-molecular-weight polymers and semi-solid or resinous solid polymers. The dimers and viscous, highmolecular-weight polymers are generally soluble in the diolefin itself or other hydrocarbons and, in certain cases, are depolymerized on heating to the original diolefin. On the other hand, the solid polymers of the type which have been referred to as cauliflower or popcorn polymer because of the resemblance, are quite insoluble in the diolefln and other hydrocarbons, are generally infusible and, when in contact with a monomer, continue to grow. As a result of such growth, distillation columns and other plant equipment where the monomer is present becomes fouled. The insidious character of this polymer lies in the fact that it is insoluble in all solvents and cannot be completely eliminated from equipment by mechanical means so that in a short time fouling and plug ing troubles recur. Even though the complete equipment is thoroughly cleaned, it is only a matter of time before residual particles of polymer will grow sufficiently to foul and plug the equipment. Two remedies were suggested, one to inhibit the initial growth of the self-propagating polymer and second, to control or stop the growth of preformed particles. Generally, the initial growth is found in most equipment and since this is so, means for controlling or stopping the growth of the preformed polymer is very desirable.

An object of this invention is to inhibit or stop the growth of a preformed self-propagating polymer. Various factors are considered to effect the growth of this resinous solid polymer. The presence of active oxygen (peroxides) in a diolefln, such as liquid butadiene, is believed to initiate the growth of a resinous solid popcorn polymer. Small amounts of air present in the system are a potential source of active oxygen. Other factors aiding'the initiation of resinous solid polymer are the presence of active oxygen with unpolished iron, rusty iron, certain other metals and an interface of liquid water. Rusty iron with water even in the absence of air and added peroxides was very efiective in initiating popcorn polymer formation. It is very diflicult, if not almost impossible, to eliminate these factors which tend to initiate popcorn polymer formation in commercial equipment, hence the importance of inhibiting or stopping the growth of the preformed polymer.

The resinous solid polymers of the popcorn variety comprise small glassy lumps surrounded by liner granular clinging masses possessing some rubbery properties. This glassy material, despite its appearance, exhibits considerable rubber-like rebound when dropped on a hard surface. It is infusible and cannot be molded even at 150 C.

-It is insoluble in ordinary solvents such as benzene, carbon tetrachloride, and methyl ethyl ketone. It exhibits a. slight solubility in hot xylene and a solution in xylene shows the presence of peroxides. Elemental analysis was 88.77% carbon 'and 11.27% hydrogen, corresponding closely to rate, indicating that additional points of growth are continuously formed as the mass increases. A fresh supply of active oxygen, which generally materially aids the initiation of popcorn polymer, is not required for its subsequent growth.

The rate of growth of two resinous polymer seeds in butadiene vapor at 60 C. is shown in the figure. Although the initial seeds were radically different in physical form, the growth followed much the same pattern. Practically linear curves of identical slopes were obtained when the logarithm of the mass was plotted against time.

Considering that the logarithm of the mass in growth varies linearly with time, then which corresponds to the following differential growth equation:

where w=mass, t=time, and 7c and c are constants. The fact that the rate is first order with respect to the mass is interpreted to mean that all portions of the polymer are in active growth and are accessible to the monomer probably as the result of permeation of the polymer by diolefin vapor or liquid. Visual observation shows that if a solid seed is exposed to diolefin vapor, it first swells, then cracks, and finally subdivides into fine granules. The granular mass continues to grow as long as monomeric vapor is supplied. If the polymer is confined in a space insuilicient to accommodate the growing polymer, high pressures are built up in the vessel. A few tests of the polymer growth in the liquid phase gave approximately the same rate of growth as in the vapor phase.

It has been customary to inhibit polymerization of diolefins by adding small amounts of antioxidant inhibitors to the monomer. It has been found that this technique is virtually inefiective in inhibiting the growth of preformed popcorn polymers even when large amounts of inhibitor are employed. This invention comprises removing the monomer from the equipment or apparatus and treating all surfaces likely to harbor particles of the polymer with a selected treating agent which may comprise a gas, vapor, liquid or solution. Treatment may be carried out at ordinary or elevated temperatures and for sufiicient time to result in reduction of the growth properties of the polymer to the desired extent or to inhibit growth until it is necessary to treat the equipment again. Our invention also comprises the use of selected treating agents. We have found that the most effective agents comprise those which attack, combine or associate chemically with aliphatic unsaturated hydrocarbons, including vulcanizing agents and accelerators for hydrocarbon rubbers, and/or those which primarily destroy peroxides, as presented in the attached table. Certain of the agents undoubtedly have both functions. Moreover, the effectiveness of an agent as an inhibitor for the growth of popcorn polymer may be related to the degree to which the agent in question pursues either or both of these chemical behaviors. It has become apparent to the inventors that the presence of active double bonds and/or active oxygen (peroxides) is necessary for the autocatalytic growth of the polymer; and

moreover, that destruction or partial destruction of these components of the polymer is tantamount to the inhibition of polymer propagation. The

invention should not be bound by any theory of the action of these agents, however. Neither should the classification of effective agents as outlined in the attached table be limited by any theory as to the mode of action of the agent toward the polymer or toward reactive chemical molecular groups within the polymer molecule. Action of some agents is undoubtedly by addition to the carbon-carbon double bond, others by virtue of action on the alpha carbon atom which is activated by the presence of the adjacent double bond. By vulcanizing agents and accelerators as a class it is implied substances which are capable of vulcanizing unsaturated hydrocarbon polymers or are capable of catalyzing the vulcanization action employing sulfur as the agent. It is postulated that such action takes place by cross-linking of double bonds between unsaturated polymer chains or by cross-linking between groups activated by the presence of double bonds. Certain action may take place by virtue of the presence of peroxides in the polymer. Peroxides are known to oxidize oximes to nitroso-bodies which in turn can combine with unsaturated linkages. Oximes are particularly effective treating agents. The nitroso-bodies are likewise effective. The mode of operation of the oximes may not only be destruction of peroxides, but the further action of the products of the reaction (nitroso-compounds) with the polymer.

vulcanization accelerators such as tet; amethylthiuram disulfide, N-cyclohexyl-Z-benzothiazole sulfinamide, mercapto-benzothiazole in solution form were successfully used to treat the popcorn polymers-during the down period, i. e., when the monomers were separated from the polymer. The polymer seeds should be treated when they are very small because when they are relatively large it is likely that the percentage of mass effectively treated is rather small. Smaller seeds are more effectively treated. Among the vulcanizing agents, sulfur was only moderately effective, nitroso bodies more so, and quinone dioxime very effective in inhibiting polymer growth.

Of the other agents reactive toward double bonds or materials containing double bonds, cuprous ammonia acetate solution is fairly effective. Bromine and sulfur dioxide vapors have a strongly inhibitive effect.

Of the substituted phenol-type oxidation inhibitors, none is exceptionally efiective except in the presence of anhydrous aluminum chloride which is an active catalyst for alkylation of double bonds and hydrocarbon groups activated by the presence of double bonds. A sufficiently high concentration of A1013 with either tert.-butyl catechol or resorcinol is very effective. AlCla alone is only moderately effective.

As might be expected, concentrated sulfuric acid charred the seeds so that they did not grow markedly. More dilute acid did not reduce the rate as much as the concentrated acid did.

The popcorn polymer is treated with the deactivating agent during the down period, that is, while the monomer is removed from the equipment and is eparated from the popcorn polymer. It is generally desirable to remove excess of the deactivating agent from the equipment after this treatment, as by washing with a suitable solvent, such as water for the water-soluble agents, sulfuric acid, etc., and liquid hydrocarbons for the oil-soluble vulcanizing agents and the like.

The following table illustrates the effectiveness of various agents by showing the growth of the popcorn polymers with and without treatment.

Gnow'm or Burenmns Porconn PoLmre m Seruaersn Bnrsnmm: VAPOR AT 60 0. Anna Venous Tsaenmm Treating Agent Growth wt. per cent Wt. of Seed, Grams Temp. 01' Duraper g g Solvent, ii any Treat; glen, Aamty men Treated Untreated A B l Initial Final Gain seed (A) sad (B) GLASS AVULCANIZING AGENTS AND ACOELERATORS Sulinr Vanni hot 0. 0402 0. 0933 0. 0531 8 2, 270 17, 750 13 Tetramethyl-thiuram disulilde benzene .d0 0. 0294 0. 0300 0. 0000 8 12 17, 750 0. 07 N-cyglohexyM-bennothiazole suliina- -.do .-d0. 0. 0461 0. 0507 0. 0046 8 41 17, 750 0. 23

m e. Mgrmpto-benmthiaufln d0 .d0. 0. 0505 0.0626 0.0121 8 120 17, 750 0. 71 30% dinitroso-bennene in clay, 2% in ..do .do..... .0142 0. 0203 0.0061 8 296 2, 950 10 Dinitroso benzene vapors with steam. 100 0... 0. 0106 0. 0140 0. 0034 8 170 2, 950 5. 8 Quinone dioxime isopropyl alcohol. 80 0. 534 0. 0582 0. 0048 8 38 17, 750 0. 21

Do cuprous ammonia. room 0.0092 0. 0103 0. 0011 8 05 2, 950 2. 1 .d0 hot 0. 0149 0.0176 0.0027 8 94 2, 950 3.2

CLASS IB0THER SUBSTANCES WHICH ATTACK UNSATU RA'IED HYDROOARBONS Oupmua Acetate 0. 0013 8 67 2, 950 2. 3 o 0. 0007 8 83 2, 950 2. 7 Bromine vapor 0. 0425 130 17, 200 0, 76 Bulim- Dioxide Gas 0. 0010 8 8 5, 000 0. 10 t-Butylcatechol and A101; 0.0009 17 1 0 17, 200 0. 00 Resorcinal and A101- 0. 0891 10 850 17, 200 4. 9 Bulimia Acid, conc -0.0003 8 0 17, 100 0 CLASS G-SUBSTANOES -WHICH PRIlviARILY DES'i :lOY PEROXIDES Aeetoxime, 2% water hot 0. 0090 0. 0102 0. 0012 8 67 2, 950 2.3 Butyraldoxime, 2% do d0.. 0. 0285 0.0307 0.0022 8 28 5, 000 0. 56

2% .do do 0. 0190 0.0241 0.0042 8 88 17, 100 0. 51 t-Butyleetechnl benzene do..." 0. 0. 0. 0545 8 840 17, 750 4. 7 Alpha Naphthol do d0 0. 0762 0. 1708 0. 1000 5 13, 700 17, 200 80 l Seeds treated with solution or slurries oi the agent for 1 to 4 hrs., thoroughly rinsed and dried, except as noted.

i This seed was later broken in two to expose the interior to butadiene vapor; it grew 1.9% in 14 days. l The extremely wide fluctuation in the rate of growth oi the untreated seeds may be a source of error in any comparison of these seeds. 4 The growth exprewed as weight per cent per month is obtained by extrapolatmg along a straight line from the actual duration oi the test to s month's duration on plot oi log mass 0! seed versus time.

We claim:

1. A process for handling oleflnic hydrocarbons normally tending to form insoluble self-propagating polymers which eventually plug the handling equipment comprising handling said oleflnic hydrocarbons until a small amount of said selfpropagating polymer is formed, removing the oleflnic hydrocarbons from the polymer, treating the said polymer at reaction conditions in the absence of said oleflnic hydrocarbons with an agent capable of reacting therewith at said reaction conditions by addition to an olefinic linkage whereby further growth of said polymer is inhibbon with the treated growth inhibited polymer. 2. A process for handling dioleflns normally tending to form insoluble self-propagating polymers which eventually plug the handling equipited and then recontacting the oleflnic hydrocar-' is formed, removing the butadiene from the polymer, treating the said polymer in the absence of said butadiene with a. sulfur containing vulcanization accelerator whereby the further growth of said polymer is inhibited and then recontacting the diolefin with the treated polymer.

4. A process according to claim 3 in which the v REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,373,754 Fryling et a1. Apr. 17, 1945 2,402,113 Hatch et a1 June 11, 1946 2,415,009 Hatch et a1 Jan. 28, 194'! 2,425,842

Seyiried et a1. Aug. 19, 1947 

